1. Field of the Invention
This invention pertains to circuits for broad-band RF systems. More particularly, this invention pertains to modular RF (radio frequency) circuit components.
2. Description of the Prior Art
In the telecommunications industry and more particularly in the video transmission industry, broad-band radio frequency (RF) signals (i.e., 5 MHz to 1 GHz) are carried over coax conductors from a headend to consumers. At the headend of the system, numerous signals are manipulated to achieve a wide variety of functions and objectives. For example, signals carried on numerous coax cables may be combined onto a single coax conductor. Similarly, a signal on a main coax conductor may be divided into a plurality of signals carried on branch coax conductors. Additionally, signals may be added or removed from a main conductor through directional couplers or the like.
In addition to combining, splitting, diverting or adding signals, the headend will also include apparatus for modifying signals. For example, in order to adequately tune the system, it may be desirable to provide attenuators or the like to attenuate a signal to a desired level. Further, as a broadband RF signal is carried over a length of cable, the high frequency range of the signal may be attenuated more than a low frequency range of the signal. As a result, equalizers are utilized to modify the signal to have a level intensity throughout its frequency range.
Throughout the system, performance characteristics are critical. For example, a common performance criteria is to maintain the flatness of a signal. Flatness refers to maintaining a level intensity of a signal throughout its frequency range. For example, if the signal is attenuated by 2 dB at 1 Ghz, then it is desirable that the signal be attenuated at 2 dB at the 5 Mhz frequency. Further, the system needs to be tuned for impedance matching.
Prior art headends include a wide variety of devices to accommodate and accomplish the functions described above. It is desirable to provide an apparatus to accommodate the various functions required at the headend through a modular construction to permit ease of maintenance and cable management in a headend. Such a device must accommodate the performance characteristics of the headend while permitting the modular construction to enhance the cable management and organization of a headend.
According to a preferred embodiment of the present invention, a module is provided for containing a circuit for performing discrete functions on a radio frequency signal. The module comprises a housing of electrically conductive material. The housing has a front face and an opposite rear face. The front face and rear face are separated by opposite sidewalls and opposite end walls. A plurality of coax connectors are secured to the rear face with an outer shield of the connectors electrically connected to the housing. A circuit board is contained within the interior. The circuit board is generally parallel to and spaced between the sidewalls. The circuit board has a component side and a ground side. The ground side includes a layer of electrically conductive material which is electrically connected to the housing. A plurality of coax cable connection locations are provided on the ground side of the circuit board. Each of the coax cable connections includes a ground connection for connecting ground shields of coax cables to the layer of electrically conductive material. The component side of the circuit board includes a plurality of circuit components interconnected with one another and with the coax cable connection locations through a plurality of circuit paths. A plurality of coax cables are disposed within the interior and connected to individual ones of the coax connectors and the coax cable connection locations. Each of the coax cables has a ground shield connected to the outer shields of the connectors and to the ground connections of the coax cable connection locations. A plurality of cables are routed for the cables to be disposed between the ground side of the circuit board and the opposing sidewall of the housing.